Refrigeration systems are known for use with laboratory refrigerators and freezers of the type known as “high performance refrigerators” (the “high performance” label typically depending on specific limitations of peak temperature variation allowed within the refrigerator), which are used to cool their interior storage spaces to relative low temperatures such as about +4° C., about −30° C., or lower, for example. Refrigeration systems may include a single refrigerant stage circulating a refrigerant between a series of elements to remove heat energy from the interior storage spaces.
Refrigerators and freezers having two-stage cascade refrigeration systems are also known for cooling spaces such as the interior of cabinets, for example, to temperatures well below zero degrees Celsius, such as temperatures below −40° C. For example, freezers of the type known as ultra-low temperature (“ULT”) freezers are known to use this type of refrigeration system and are used to cool cabinet interiors to temperatures as low as about −80° C. or even lower. Refrigeration systems of this type are known to include two refrigeration stages circulating first and second refrigerants, respectively. The first refrigeration stage transfers energy (i.e., heat) from the first refrigerant to the surrounding environment through a condenser, while the second refrigerant of the second refrigeration stage receives energy from the cooled space (e.g., a cabinet interior) through an evaporator. Heat is transferred from the second refrigerant to the first refrigerant through a heat exchanger that is in thermal fluid communication with the two refrigeration stages of the refrigeration system. To this end, the first and second refrigeration stages collectively operate to remove a significant amount of heat energy from the cooled space, to thereby achieve the low set point temperatures described above.
As will be readily understood, the removal of a high amount of heat energy from a cabinet interior (or similar cooled space) often necessitates a lengthy pull down time upon initial cooling of the cabinet interior from ambient temperature, or after a door opening event that adds ambient heat energy back into the cabinet interior. This is true in single stage refrigeration systems as well as in the cascade refrigeration systems of ULT freezers described above. As such, it is desirable to improve the energy efficiency and responsiveness of refrigeration systems to minimize an amount of time the cabinet interior remains at elevated temperatures above the desired set point temperature during operation.
Condensers used with conventional refrigeration systems of these types can be configured to discharge heat energy to air, water, or some other medium representing the ambient environment. Water-cooled condensers are known from several prior art references, including U.S. Pat. No. 5,689,966 to Zess et al.; U.S. Pat. No. 9,404,679 to Ito et al.; and U.S. Patent Publication No. 2012/0291478 to Kim et al., for example. These prior art references have achieved improvements in the efficiency of heat discharge at the condensers by transferring the heat energy to water flowing in a separate cooling circuit. However, further improvements in efficiency and temperature responsiveness beyond just water cooling in a condenser remain desirable in this field.
To this end, of the known examples of water-cooled condensers including those Patents identified above, only the Zess Patent (U.S. Pat. No. 5,689,966) describes that the water used to remove heat energy at the condenser may also be used in another heat exchanger. To this end, the water in FIG. 4 of the Zess Patent is used as a further heat discharge downstream from the condenser to receive heat energy stemming from a de-superheater heat exchanger and via another intermediate coolant circuit extending between the water circuit and the de-superheater heat exchanger in that refrigeration system. However, water used for such additional step(s) of heat discharge at the specified temperatures becomes subject to calcium carbonate deposits, which can then build up in the water circuit and diminish heat transfer performance/efficiency. Therefore, this type of arrangement has not been adopted as an effective solution for providing long-term improved efficiency and temperature responsiveness in refrigeration systems.
There thus remains a need for further improvements in refrigeration systems, including those with water-cooled condensers, which address these and other deficiencies of the known designs.